The purpose of this contract is to provide research and development support for the Unified Medical Language System. Specifically, the contractor will support (1) the definition of the functional components and algorithms needed: to relate the user's terms to information in the UMLS Knowledge Sources; to interact with the user to clarify the information needed; and to select and access the information sources relevant to the user's inquiry, and (2) the evaluation of the utility of the UMLS Knowledge Sources and proposed functional components in a variety of environments.